feat(card-master): add request/response DTOs for /immutable_data/card_master

SVSim.EmulatedEntrypoint/Models/Dtos/Responses/ImmutableData/CardMasterResponse.cs

@@ -0,0 +1,17 @@
+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Responses.ImmutableData;
+
+/// <summary>
+/// Wire response shape. Client decodes <c>card_master</c> via:
+/// <c>Convert.FromBase64String</c> → <c>GZipStream.UncompressBuffer</c> → UTF-8 decode →
+/// <c>JsonMapper.ToObject</c>, yielding a dict <c>{ "1": "&lt;csv&gt;", "2"?: "&lt;csv&gt;" }</c>.
+/// </summary>
+[MessagePackObject]
+public class CardMasterResponse
+{
+    [JsonPropertyName("card_master")]
+    [Key("card_master")]
+    public string CardMaster { get; set; } = "";
+}